Conventionally, an ultrasound diagnosis apparatus is on a smaller scale than other medical image diagnosis apparatuses such as an X-ray diagnosis apparatus, an X-ray computed tomography (CT) apparatus, and a magnetic resonance imaging (MRI) apparatus. In addition, because it is an apparatus that can display in real time the movement of an examination target such as cardiac pulsation and fetal activity by a simple operation of placing an ultrasound probe on the surface of the body, the ultrasonic diagnosis apparatus plays an important role in the present medical practice. Moreover, ultrasound diagnosis apparatuses that are secure from radiation exposure include downsized ones so that they can be carried with one hand. Such ultrasound diagnosis apparatuses can be readily used in medical settings such as obstetrics and home healthcare.
The ultrasound diagnosis apparatus emits ultrasound waves from its ultrasound probe into the patient's body. Then, the ultrasound diagnosis apparatus receives, with the ultrasound probe, reflection waves caused by acoustic impedance mismatching inside the body of the patient, and generates a reception signal. The ultrasound probe is provided with multiple piezoelectric vibrators in the scanning direction to transmit and receive such ultrasound waves. These piezoelectric vibrators are piezoelectrically polarized in the directions of the ultrasound wave transmission and reception, generating ultrasound waves based on a transmission signal and generating a reception signal upon receiving reflection waves.
With the conventional technology, however, depolarization caused in the piezoelectric vibrators tend to lower the performance of the ultrasound probe.